In many applications, for example, in the communications or radar fields it is desirable to provide devices for identifying the characteristics of incoming signals, particularly with respect to the characteristics of a reference signal. Such devices act as matched filters for such purposes. Moreover, it is desirable that such filter devices be adaptive in the sense that changes in the characteristics of the reference signal can be readily made and the filter thereby adapted to identify incoming signals with respect to the changed characteristics.
Certain techniques, such as the utilization of digital computer processing, have been used to provide appropriate adaptive matched filtering operation so that an appropriate correlation between an incoming signal and a reference signal to provide a matched filter output is achieved. Such techniques provide what is often called adaptive, or programmable, correlation. Up to the present time, however, no one has designed a surface wave device for providing a continuously programmable correlator operation unrestricted except by correlation time and bandwidth, despite the obvious need for such devices in many applications. Such devices can be contrasted with delay line devices using discrete switchable taps, which devices are programmable only at discrete points as described in the article of Hagon et al., "Integrated Programmable Analog Matched Filters for Spread Spectrum Applications", 1973 Ultrasonics Symposium Proceedings, IEEE, New York, New York, pp. 333-335.